The lining of aircraft interiors primarily consists of sandwich structures with a honeycomb core, for example, of a resin-impregnated aramid fiber material and cover layers of glass fiber prepreg and/or carbon fiber prepreg. In order to provide a certain sound insulation, it is advisable to realize these sandwich structures such that they are not completely closed, but rather also allow sufficient gas permeability. This means that fluids such as, for example, condensation water also penetrate into the cells or honeycombs of the core layer. However, penetrating water could lead to corrosion or rotting of the materials of the composite panel.
DE 10 2006 023294 A1 introduces a composite panel that is designed for sound insulation purposes and simultaneously allows sufficient drainage such that rotting phenomena do not occur. To this end, a composite panel is proposed that features two cover layers and a core layer arranged in between, wherein the first cover layer features a draining layer and the cells of the core layer are at least partially covered by the draining layer.
In order to evaluate the impact resistance of a material/substance/semi-finished product (in the following description, the terms “substance” or “material” also refer to a “semi-finished product”) for use in an aircraft, it is common practice to carry out impact stress tests, in which test bodies of predefined dimensions are dropped on a material to be tested, for example, from predefined heights. In addition to high velocity impact tests, there also exist low velocity impact tests (also referred to as “low velocity impact tests” exerting an impact energy of 2 joule or more) that make it possible to assess if a material may be used, for example, in special areas of the interior of an aircraft cargo hold. The problem with the above-described composite panel with cover layers of lightweight glass fiber/carbon fiber prepregs may be seen in that they would not withstand a low velocity impact test with impact energy of 2 joule more. The energy that may be absorbed by a thusly structured material is so low that the composite panel would simply be destroyed during such a low velocity impact test and at least feature an unacceptable hole at the point of impact.
Furthermore, lining parts ready to be installed in an aircraft should have a specific weight of no more than about 950-1150 g/m2, wherein this value represents the state of the art with respect to closed lining panels. Currently, the specific weight of the lightest, sufficiently gas-permeable lining panels in the form of lining parts ready to be installed in an aircraft that withstand a low velocity impact test with impact energy of 2 joule or more and consist of glass fiber-reinforced and/or carbon fiber-reinforced plastic lies at approximately 1400 g/m2 without a textile layer applied thereon. However, this is unacceptable.
It was furthermore determined during the investigation of the above-described composite panels that no sufficient drainage is achieved in a horizontal installation position. Consequently, it may be expected that water absorption due to cleaning and condensation effects will result in at least 40 percent by volume of the core material remaining filled with water until it is evaporated or released due to strong vibrations as they occur, for examples during the start of the aircraft.